A federal judge on Friday ordered Massachusetts Attorney General Maura Healey to come to Texas next month to be deposed in Exxon Mobil Corp's lawsuit over her office's climate change probe.

The judge also asked New York Attorney General Eric Schneiderman to be available to come to Dallas next month to testify in the same case.

The two Democratic politicians are defendants in Exxon's lawsuit accusing them of unlawfully exercising their powers in their investigations into whether the oil giant misled investors and the public by downplaying the impact of global warming.

The company is seeking an injunction barring the enforcement of subpoenas the attorneys general issued demanding documents relating to climate change research and investor communications stretching back decades.

The judge is deciding whether to summon Mr. Schneiderman to Texas as well. Friday's order, essentially a save-the-date, advised the New York attorney general to reserve Dec. 13 for giving testimony in Dallas. The judge scheduled Ms. Healey's deposition for the same day.

"The Court is mindful of the busy schedule of each of the Attorneys General Healey and Schneiderman and will be open to considering a different date for the deposition," wrote Judge Kinkeade.

A spokeswoman for Ms. Healey said the office was "surprised" the judge summoned the attorney general to Dallas, which is about 1,750 miles from Boston.

The office, she said, still vows "to fight aggressively to investigate whether Exxon Mobil deceived consumers and investors about the impact of fossil fuels." A spokesman for Mr. Schneiderman said the office "will respond appropriately."

Exxon said Judge Kinkeade's order "reinforces" his October ruling granting discovery.

"We have no choice but to defend ourselves against politically motivated investigations that are biased, in bad faith and without legal merit," a company statement said. "We did not start this, but we will see it through."

Exxon's complaint accuses the attorneys general of improperly coordinating with lobbyists and plaintiffs' lawyers in an effort "to silence and intimidate one side of the public policy debate on how to address climate change."